1. Field of the Invention
This invention generally relates to a method for enhancing biotransformation of groundwater contaminants, and in particular to a method for enhancing biotransformation of chlorinate organic compounds in groundwater.
2. Description of the Related Art
In order to enhance biotransformation of groundwater contaminants, it used to provide additional nutrient sources, electron donors, pH buffer solvents and the likes into groundwater through circulation wells to increase the in-situ degradation of groundwater contaminants by metabolic activity of microorganisms. Also, in order to enhance the contaminants desorbing from soil, surfactants are added to increase the solubility of the contaminants in groundwater.
The chlorinated aliphatic hydrocarbons have properties including high oil solubility, low flammability, low explosibility, high density vapor, chemical stability, low boiling point and high vapor pressure so that it is widely used in variety of industrial fields. However, left and untreated chlorinated aliphatic hydrocarbons waste are some of the most common and potentially hazardous soil and ground water contaminants. For example, chlorinated aliphatic hydrocarbons such as perchloroethylene (PCE) may form dense nonaqueous phase liquid (DNAPL) in groundwater because it is denser than water and it has high viscosity that may cause it is hard to remove from groundwater.
Some methods for treatment of groundwater contaminants involve physic methods such as sucking, purging and adsorption. However, these methods can not effectively and completely remove the contaminants above an impervious zone because of the uncertain scope of contaminated sources. Moreover, these methods only pump out but not treat the contaminants. Chemical oxidation may use oxidants for oxidizing the chlorinated aliphatic hydrocarbons. Due to the non-selective characteristics of oxidants, the oxidants commonly oxidize natural soil oxidizable matters prior to the chlorinated aliphatic hydrocarbons. Accordingly, the economic efficiency of the chemical oxidation is low. Currently, biotransformation of groundwater contaminants using microorganisms has become a favorable alternative for treating groundwater contaminants.
From a viewpoint of chemical reaction, PCE is liable to receive electrons but not release electrons, since it is a substance with highly oxidized state. Therefore, the biodegradation of PCE has a priority step of reductive dechlorination. Currently, some commercial biological agents have been employed to increase the transformation of PCE. However, the commercial biological agents are expensive. There is a need to seek an additive as cheap surfactant and an electron donor to increase the solubility and biodegradation of PCE in groundwater.
Therefore, the inventor conducted researches according to the scientific approach in order to improve and resolve the above drawback, and finally proposed the present invention, which is reasonable and effective.